2007 Silverado 6.0L Multiple Misfire Codes: Diagnosis & Fix

Your 2007 Silverado 6.0L has a misfire on cylinder 6 (P0306), a likely ABS wheel speed sensor issue (C0321), and a body control module diagnostic trouble code (C0561). The misfire is the priority and is often caused by a failed ignition coil or fuel injector.

For a shop to diagnose and repair the misfire, expect $400 to $800, with about 1.5 hours of labor. A DIY fix with a coil (GM part #12640421) and plug is under $150 and takes about 30 minutes if you’re handy.

Swap the coil from cylinder 6 with another cylinder, clear the codes, and see if the misfire moves to diagnose it yourself.

For specific year variations and engine codes, see the detailed sections below.

What Code Means

Diagnosing a 2007 Silverado 1500 6.0L with Codes P0306, C0321, and C0561

This is a common, interconnected set of codes on this platform. Here is a simple breakdown of what each means and how they are typically related.

P0306: This is your root problem. This is a Misfire Detected on Cylinder #6. The engine control module (ECM) has sensed that cylinder 6 is not firing properly. Common causes for a single-cylinder misfire on the GM 6.0L (LQ4/LQ9) include:

• A failed ignition coil (GM Part # 12573190). Cost: ~$85-$110 each.
• A worn or fouled spark plug (ACDelco 41-110). Cost: ~$10-$15 each.
• A faulty fuel injector (GM Part # 12580662). Cost: ~$120-$150 each.
• Less commonly, low compression in cylinder 6 due to a mechanical issue.

Diagnosis starts here. Swap the coil from cylinder 6 with cylinder 5. Clear codes and see if the misfire moves to P0305. If it does, you need a new coil. Labor: ~0.5 hours for diagnosis/coil replacement.

C0321: ABS/TCS Module Malfunction. This code in the ABS module is often a direct result of the engine misfire (P0306). The stability control system detects the erratic engine operation and disables traction control (you’ll likely see the “Service Traction System” message). Fixing the engine misfire (P0306) will usually allow this code to be cleared and the system to return to normal.

C0561: System Disabled Information. This is a generic chassis code that typically sets alongside C0321. It simply confirms that a stability control function has been disabled due to the detected fault (the misfire). Like C0321, it is a symptom, not a cause.

Action Plan:

1. Focus entirely on diagnosing and fixing the P0306 cylinder 6 misfire first. Perform the coil swap test.
2. After repairing the misfire, clear all codes.
3. Drive the truck. The ABS/TCS codes (C0321, C0561) should not return if the misfire is resolved.

Ignoring the misfire can damage the catalytic converter. Total repair cost, if it’s just one coil and plugs, is typically $250-$400 including 1.0-1.5 hours of labor.

Causes

Diagnostic Overview: A 2007 Silverado 1500 with the 6.0L (LQ4/LQ9) engine throwing P0306 (Cylinder 6 Misfire), C0321 (ABS/TCS Serial Data Circuit Malfunction), and C0561 (System Disabled Information Stored) indicates a primary engine issue causing secondary system disables. The ABS/Stabilitrak system (C0321/C0561) often disables itself when it detects a severe engine misfire to prevent erratic vehicle behavior. Therefore, focus must be on the root cause of the P0306.

Primary Cause: Ignition System Failure (Coil or Plug)

Engineering Reason & Failure Mode: The Gen IV 6.0L uses individual coil-on-plug (COP) ignition. The coil for cylinder #6 (GM part number 12573190) is a common failure point. Internal winding breakdown or carbon tracking from moisture intrusion causes an intermittent or complete loss of spark. The spark plug (ACDelco 41-110) can also fail due to worn electrodes or cracked porcelain. This is the most frequent cause of an isolated misfire code. Diagnosis involves swapping the #6 coil with another cylinder and seeing if the misfire follows the coil.

Secondary Cause: Fuel Injector Fault

Engineering Reason & Failure Mode: The Multec 2 fuel injector (GM part number 12568354) for cylinder #6 can fail electrically (open or shorted circuit) or mechanically (clogged or stuck pintle). A clogged injector starves the cylinder of fuel, while a leaking one floods it. Both result in incomplete combustion. Electrical failure is often due to heat cycling degrading the injector solenoid windings. Testing involves checking injector circuit resistance (should be 10-14 ohms) and performing a balance test.

Tertiary Cause: Mechanical Compression Loss

Engineering Reason & Failure Mode: A loss of sealing in cylinder #6 leads to low compression. Common failures include a worn or damaged exhaust valve (due to heat stress and seat recession common in these engines) or a failed valve spring. A broken spring or a worn camshaft lobe on the #6 cylinder can also cause this. This requires a mechanical compression test (healthy engine should show 150+ psi per cylinder with less than 10% variation).

Supporting Cause: Faulty Wiring or Connector

Engineering Reason & Failure Mode: The wiring harness to the #6 coil or injector runs near the hot exhaust manifold. Over time, the insulation can brittle and chafe, causing a short to ground or an open circuit. The connector itself can suffer from terminal corrosion or loose pins, leading to an intermittent connection. This requires a thorough visual inspection and a voltage drop test of the control and power circuits.

Initial Action: Start with a visual inspection of the #6 coil and wiring. Swap the coil with another cylinder, clear codes, and test drive. If the misfire moves, replace the coil. If not, proceed to check fuel delivery and compression.

Diagnosis

Diagnostic Guide: 2007 Silverado 1500 6.0L with P0306, C0321, C0561

Vehicle Specific: This guide applies only to the 2007 Chevrolet Silverado 1500 with the 6.0L V8 (LQ4/LQ9) engine and 4L80-E transmission.

Initial Quick Checks (First 30 Minutes)

1. Code Definition & Battery:
P0306 is a misfire on cylinder #6 (driver’s side, rear).
C0321 is a ABS/TCS code for a steering sensor circuit malfunction.
C0561 is a system voltage code, often related to low battery voltage or a failing battery.
Action: Test battery voltage. Key-on, engine-off should be 12.4V+. Running should be 13.5-14.8V. A weak battery (<12.2V) can cause all these codes simultaneously.

2. Visual & Basic Mechanical for P0306:
– Inspect the #6 spark plug (GM part # 12571164) and coil boot for damage or carbon tracking.
– Swap the #6 ignition coil with another cylinder (e.g., #2). Clear codes and test drive. If the misfire moves (e.g., P0302), the coil is faulty (GM part # D585, approx. $85-$120).
– Check for obvious vacuum leaks, especially at the intake manifold gasket (common failure). Listen for hissing near the rear of the intake on the driver’s side.

3. Steering Sensor for C0321:
Perform a simple steering angle relearn. On a level surface, start the truck, turn the steering wheel lock-to-lock, then center it. Shut off for 30 seconds. This can clear a spurious C0321 if no hard fault exists.

Deeper System Inspection

If Quick Checks Don’t Resolve Issues:

1. Misfire Diagnosis (P0306):
– Perform a relative compression test with a scan tool to rule out mechanical issues (broken valve spring, worn cam lobe).
– Test fuel injector #6 (GM part # 12580654). Swap it with another cylinder. If the misfire moves, replace the injector. Labor: ~1.8 hours for intake manifold removal/injector service.
– Check for proper compression on cylinder #6 (should be 150+ psi and within 10% of other cylinders).
– Inspect the intake manifold gasket (GM part # 12585427) for leaks at the rear driver’s side. A smoke test is definitive.

2. ABS/Steering Angle Sensor (C0321):
– With a scan tool capable of reading ABS module data, monitor the Steering Wheel Position Sensor signal while turning the wheel. It should change smoothly from 0 to 360 degrees.
– Common failure is the clock spring/sensor assembly (GM part # 25962639) within the steering column. Labor: ~1.5 hours for diagnosis and replacement.

3. Electrical System (C0561):
– Load test the battery. Replace if it fails.
– Check for corrosion at the battery cables, ground points (especially G102 on the driver’s side cylinder head), and the B+ connection at the underhood fuse block.
– Test the alternator output under load (headlights on, A/C on high). It must maintain above 13.5V.

Probable Root Cause & Repair Cost Estimate

On this vintage Silverado, these codes appearing together often point to a failing battery or poor charging system causing low voltage, which disrupts the sensitive electronics in the ignition (causing misfire) and the ABS module (causing sensor codes).

Typical Repair Scenario:
1. Battery Replacement: $220 (part & labor)
2. Ignition Coil for #6: $110 (part & labor)
3. Steering Angle Sensor/Clock Spring: $450 (part & labor)
Total Estimate Range: $250 – $800+ depending on the root cause found during diagnosis.

Master Tech Advice: Always start with the battery and charging system. Diagnose the P0306 misfire thoroughly before condemning the steering sensor, as the C0321 may clear after a stable voltage is restored.

Cost

This is a classic combination of codes on the 2007 Silverado 6.0L (LQ4/LQ9). The P0306 (cylinder 6 misfire) is your primary drivability issue, likely caused by the root problem indicated by C0321. C0561 is a secondary symptom.

• P0306: Misfire on cylinder 6.
• C0321: Left Rear Wheel Speed Sensor Circuit Malfunction. This is your key. On this generation, a faulty wheel speed sensor or its wiring can cause the ABS module to send erratic signals, which the PCM misinterprets as engine misfires, setting P0306.
• C0561: System Disabled Information. This is set because the ABS/Stabilitrak system has detected the C0321 fault and has partially disabled itself.

Most Likely Repair: Replace the left rear wheel speed sensor and inspect/repair its harness, especially where it runs along the frame rail. This often fixes all three codes.

Item	DIY Cost (Est.)	Professional Shop Cost (Est.)	Notes & Part Numbers
Left Rear Wheel Speed Sensor	$45 – $85	$65 – $120 (part markup)	GM Part # 25795867 (ACDelco #171-1366). Aftermarket options are available for less.
Labor	$0	$120 – $180 (1.0 – 1.5 hrs)	Shop labor rate assumed at $120/hr. The repair involves removing the wheel, unbolting the sensor from the rear differential housing.
Diagnostic Fee	$0 (Your own scan tool)	$150 – $200	This is critical. A proper diagnosis should link the ABS code to the misfire. This fee is often waived if you proceed with the repair.
Potential Additional Parts	$20 – $100	$40 – $150	If the harness is damaged, you may need a repair pigtail (GM #15333077). In rare cases, a failing ABS module itself can cause this, but rule out the sensor first.
TOTAL ESTIMATED COST	$65 – $185	$335 – $650+	DIY assumes you have basic tools and follow a repair guide. Shop cost includes diagnosis and repair.

Technician’s Advice: Before replacing anything, perform a visual inspection of the left rear wheel speed sensor wiring from the connector at the frame to the sensor on the differential. Look for chafing, cuts, or damage. This is a very common failure point on these trucks. If the wiring is intact, replacing the sensor (GM #25795867) is the correct first step. Clear all codes after repair and perform a test drive.

Fix

2007 Silverado 1500 6.0L (LQ4/LQ9) – Diagnostic & Repair for P0306, C0321, C0561

This combination of codes points to a misfire on cylinder 6 (P0306) compounded by ABS/brake system communication issues (C0321, C0561). The ABS codes often appear after repeated misfire events. The primary focus must be diagnosing and fixing the misfire first, as it is the root cause.

Tools & Parts Needed

• Scan Tool (capable of viewing misfire counters & ABS codes)
• Basic Hand Tools (sockets, ratchet, extensions)
• Spark Plug Socket (5/8″ or 16mm, magnetic preferred)
• Torque Wrench (inch-lbs and ft-lbs)
• Compression Tester (optional but recommended)
• NOID Light or Test Light
• Dielectric Grease
• Potential GM Parts:
  • Spark Plug: AC Delco 41-110 (Iridium) – ~$8 ea.
  • Ignition Coil: GM 12573190 (D585) – ~$65
  • Fuel Injector: GM 12580654 (for cylinder 6) – ~$120
  • Ignition Coil Boot/Spring Kit: GM 12579265 – ~$12

1. Initial Diagnosis & Safety

   Clear all codes. Start the engine and monitor the scan tool’s Mode $06 data for misfire counters on cylinder 6. Verify P0306 returns. Note if the misfire is present at idle, under load, or both. This guides the next steps.

2. Visual Inspection & Swap Test (1.0 hr labor)

   With the engine off, inspect the #6 ignition coil (driver’s side, second from front) and its wiring for damage. Perform a component swap. Swap the #6 coil with #2 coil. Swap the #6 spark plug with #2. Clear codes, run engine, and recheck misfire counters. If the misfire moves to cylinder 2, the swapped part is faulty. If it stays on #6, the issue is with the fuel injector, compression, or wiring.

3. Check Fuel Injector Operation (0.5 hr labor)

   If misfire stayed on #6, test the fuel injector. Unplug the #6 injector connector (gray latch). Using a NOID light, check for a pulsed signal with the engine cranking. No pulse indicates a wiring/ECM issue. A good pulse suggests a clogged or faulty injector. Listen for a clicking sound with a mechanic’s stethoscope.

4. Compression & Mechanical Check (0.7 hr labor)

   If ignition and fuel checks are good, perform a wet/dry compression test on cylinder 6. Specification is 120-170 psi, with less than 10% variation between cylinders. Low compression indicates a mechanical fault (worn rings, valve issue).

5. Repair & Replacement

   Based on your findings:
   
   For Coil: Replace with GM 12573190. Apply dielectric grease to the coil boot terminal. Torque the coil bolt to 89 in-lbs (7.4 ft-lbs).
   
   For Spark Plug: Replace with AC Delco 41-110. Torque to 11 ft-lbs (132 in-lbs). Do not over-tighten.
   
   For Fuel Injector: Replace with GM 12580654. Replace the upper and lower O-rings (lubricate with engine oil). Torque the fuel rail bolts to 18 ft-lbs.

6. Final Steps & ABS Code Resolution

   After repairing the misfire, clear all codes. Test drive the truck for at least 10 minutes, ensuring the misfire monitor runs. The P0306 should not return. The ABS codes (C0321 – Loss of EBCM Serial Data; C0561 – ECU Malfunction) are likely history codes triggered by the rough-running engine. They will often clear permanently after several drive cycles with the misfire fixed. If they persist, a separate ABS diagnostic is required, but this is uncommon once the engine runs smoothly.

Total Estimated Repair Cost: If only a coil and plug are needed, parts are ~$80 and labor is ~2.2 hours ($220-$330). With a fuel injector, parts rise to ~$200 and labor to ~3 hours ($300-$450). Always diagnose thoroughly before replacing parts.

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